Pretreatment compositions and methods for coating a metal substrate

ABSTRACT

Disclosed are methods for treating metal substrates, including ferrous substrates, such as cold rolled steel and electrogalvanized steel. The methods include contacting the substrate with a pretreatment composition that includes: (a) a group IIIB and/or IVB metal; (b) free fluorine; (c) a metal fluoride salt formed from a metal which forms a fluoride salt having a pK sp  of at least 11; and (d) water.

FIELD OF THE INVENTION

The present invention relates to pretreatment compositions and methodsfor coating a metal substrate, including ferrous substrates, such ascold rolled steel and electrogalvanized steel. The present inventionalso relates to coated metal substrates.

BACKGROUND INFORMATION

The use of protective coatings on metal substrates for improvedcorrosion resistance and paint adhesion is common. Conventionaltechniques for coating such substrates include techniques that involvepretreating the metal substrate with a phosphate conversion coating andchrome-containing rinses. The use of such phosphate and/orchromate-containing compositions, however, imparts environmental andhealth concerns.

As a result, chromate-free and/or phosphate-free pretreatmentcompositions have been developed. Such compositions are generally basedon chemical mixtures that in some way react with the substrate surfaceand bind to it to form a protective layer. For example, pretreatmentcompositions based on a group IIIB or IVB metal compound have recentlybecome more prevalent. Such compositions often contain a source of freefluorine, i.e., fluorine that is isolated in the pretreatmentcomposition as opposed to fluorine that is bound to another element,such as the group IIIB or IVB metal. Free fluorine can etch the surfaceof the metal substrate, thereby promoting deposition of a group IIIB orIVB metal coating. Nevertheless, the corrosion resistance capability ofthese pretreatment compositions has generally been significantlyinferior to conventional phosphate and/or chromium containingpretreatments.

As a result, it would be desirable to provide methods for treating ametal substrate that overcome at least some of the previously describeddrawbacks of the prior art, including the environmental drawbacksassociated with the use of chromates and/or phosphates. Moreover, itwould be desirable to provide methods for treating metal substrate that,in at least some cases, imparts corrosion resistance properties that areequivalent to, or even superior to, the corrosion resistance propertiesimparted through the use of phosphate conversion coatings. It would alsobe desirable to provide related coated metal substrates.

SUMMARY OF THE INVENTION

In certain respects, the present invention is directed to compositionsfor treating a metal substrate. These compositions comprise: (a) a groupIIIB and/or IVB metal; (b) an electropositive metal; (c) 0.1 to 300parts per million (“ppm”) of free fluorine; (d) a metal fluoride saltformed from a metal which forms a fluoride salt having a pK_(sp) of atleast 11; and (e) water. The composition, in certain embodiments, issubstantially free of heavy metal phosphate, such as zinc phosphate, andchromate.

In still other respects, the present invention is directed to methodsfor treating a metal substrate comprising contacting the substrate witha pretreatment composition comprising: (a) a group IIIB and/or IVBmetal; (b) an electropositive metal; (c) free fluorine; (d) a metalfluoride salt formed from a metal which forms a fluoride salt having apK_(sp) of at least 11; and (e) water, wherein the metal that forms themetal fluoride salt having a pK_(sp) of at least 11 is supplied in anamount sufficient to maintain the level of free fluorine in thecomposition to no less than 0.1 ppm and no more than 300 ppm.

In yet other respects, the present invention is directed to compositionsfor treating a metal substrate that comprise: (a) a group IIIB and/orIVB metal; (b) 0.1 to 300 ppm of free fluorine; (c) a metal fluoridesalt formed from a metal which forms a fluoride salt having a pK_(sp) ofat least 11; and (d) water. These compositions of the present inventionare substantially free of phosphate ions and chromate.

The present invention is also directed to substrates treated thereby.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of the following detailed description, it is to beunderstood that the invention may assume various alternative variationsand step sequences, except where expressly specified to the contrary.Moreover, other than in any operating examples, or where otherwiseindicated, all numbers expressing, for example, quantities ofingredients used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances.

As previously mentioned, certain embodiments of the present inventionare directed to methods for treating a metal substrate. Suitable metalsubstrates for use in the present invention include those that are oftenused in the assembly of automotive bodies, automotive parts, and otherarticles, such as small metal parts, including fasteners, i.e., nuts,bolts, screws, pins, nails, clips, buttons, and the like. Specificexamples of suitable metal substrates include, but are not limited to,cold rolled steel, hot rolled steel, steel coated with zinc metal, zinccompounds, or zinc alloys, such as electrogalvanized steel, hot-dippedgalvanized steel, galvanealed steel, and steel plated with zinc alloy.Also, aluminum alloys, aluminum plated steel and aluminum alloy platedsteel substrates may be used. Other suitable non-ferrous metals includecopper and magnesium, as well as alloys of these materials. Moreover,the metal substrate being coating by the methods of the presentinvention may be a cut edge of a substrate that is otherwise treatedand/or coated over the rest of its surface. The metal substrate coatedin accordance with the methods of the present invention may be in theform of, for example, a sheet of metal or a fabricated part.

The substrate to be treated in accordance with the methods of thepresent invention may first be cleaned to remove grease, dirt, or otherextraneous matter. This is often done by employing mild or strongalkaline cleaners, such as are commercially available and conventionallyused in metal pretreatment processes. Examples of alkaline cleanerssuitable for use in the present invention include Chemkleen 163,Chemkleen 177, and Chemkleen 490MX, each of which are commerciallyavailable from PPG Industries, Inc. Such cleaners are often followedand/or preceded by a water rinse.

As previously indicated, certain embodiments of the present inventionare directed to methods treating a metal substrate that comprisecontacting the metal substrate with a pretreatment compositioncomprising a group IIIB and/or IVB metal. As used herein, the term“pretreatment composition” refers to a composition that upon contactwith the substrate, reacts with and chemically alters the substratesurface and binds to it to form a protective layer.

Often, the pretreatment composition comprises a carrier, often anaqueous medium, so that the composition is in the form of a solution ordispersion of a group IIIB or IVB metal compound in the carrier. Inthese embodiments, the solution or dispersion may be brought intocontact with the substrate by any of a variety of known techniques, suchas dipping or immersion, spraying, intermittent spraying, dippingfollowed by spraying, spraying followed by dipping, brushing, orroll-coating. In certain embodiments, the solution or dispersion whenapplied to the metal substrate is at a temperature ranging from 60 to150° F. (15 to 65° C.). The contact time is often from 10 seconds tofive minutes, such as 30 seconds to 2 minutes.

As used herein, the term “group IIIB and/or IVB metal” refers to anelement that is in group IIIB or group IVB of the CAS Periodic Table ofthe Elements as is shown, for example, in the Handbook of Chemistry andPhysics, 63^(rd) edition (1983). Where applicable, the metal themselvesmay be used. In certain embodiments, a group IIIB and/or IVB metalcompound is used. As used herein, the term “group IIIB and/or IVB metalcompound” refers to compounds that include at least one element that isin group IIIB or group IVB of the CAS Periodic Table of the Elements.

In certain embodiments, the group IIIB and/or IVB metal compound used inthe pretreatment composition is a compound of zirconium, titanium,hafnium, yttrium, cerium, or a mixture thereof. Suitable compounds ofzirconium include, but are not limited to, hexafluorozirconic acid,alkali metal and ammonium salts thereof, ammonium zirconium carbonate,zirconyl nitrate, zirconium carboxylates and zirconium hydroxycarboxylates, such as hydrofluorozirconic acid, zirconium acetate,zirconium oxalate, ammonium zirconium glycolate, ammonium zirconiumlactate, ammonium zirconium citrate, and mixtures thereof. Suitablecompounds of titanium include, but are not limited to, fluorotitanicacid and its salts. A suitable compound of hafnium includes, but is notlimited to, hafnium nitrate. A suitable compound of yttrium includes,but is not limited to, yttrium nitrate. A suitable compound of ceriumincludes, but is not limited to, cerous nitrate.

In certain embodiments, the group IIIB and/or IVB metal compound ispresent in the pretreatment composition in an amount of at least 10 ppmmetal, such as at least 100 ppm metal, or, in some cases, at least 150ppm metal (measured as elemental metal). In certain embodiments, thegroup IIIB and/or IVB metal compound is present in the pretreatmentcomposition in an amount of no more than 5000 ppm metal, such as no morethan 300 ppm metal, or, in some cases, no more than 250 ppm metal(measured as elemental metal). The amount of group IIIB and/or IVB metalin the pretreatment composition can range between any combination of therecited values inclusive of the recited values.

In certain embodiments, the pretreatment composition also comprises anelectropositive metal. As used herein, the term “electropositive metal”refers to metals that are more electropositive than the metal substrate.This means that, for purposes of the present invention, the term“electropositive metal” encompasses metals that are less easily oxidizedthan the metal of the metal substrate that is being treated. As will beappreciated by those skilled in the art, the tendency of a metal to beoxidized is called the oxidation potential, is expressed in volts, andis measured relative to a standard hydrogen electrode, which isarbitrarily assigned an oxidation potential of zero. The oxidationpotential for several elements is set forth in the table below. Anelement is less easily oxidized than another element if it has a voltagevalue, E*, in the following table, that is greater than the element towhich it is being compared.

Element Half-cell reaction Voltage, E* Potassium K⁺ + e → K −2.93Calcium Ca²⁺ + 2e → Ca −2.87 Sodium Na⁺ + e → Na −2.71 Magnesium Mg²⁺ +2e → Mg −2.37 Aluminum Al³⁺ + 3e → Al −1.66 Zinc Zn²⁺ + 2e → Zn −0.76Iron Fe²⁺ + 2e → Fe −0.44 Nickel Ni²⁺ + 2e → Ni −0.25 Tin Sn²⁺ + 2e → Sn−0.14 Lead Pb²⁺ + 2e → Pb −0.13 Hydrogen 2H⁺ + 2e → H₂ −0.00 CopperCu²⁺ + 2e → Cu 0.34 Mercury Hg₂ ²⁺ + 2e → 2Hg 0.79 Silver Ag⁺ + e → Ag0.80 Gold Au³⁺ + 3e → Au 1.50

Thus, as will be apparent, when the metal substrate comprises one of thematerials listed earlier, such as cold rolled steel, hot rolled steel,steel coated with zinc metal, zinc compounds, or zinc alloys, hot-dippedgalvanized steel, galvanealed steel, steel plated with zinc alloy,aluminum alloys, aluminum plated steel, aluminum alloy plated steel,magnesium and magnesium alloys, suitable electropositive metals forinclusion in the pretreatment composition include, for example, nickel,copper, silver, and gold, as well mixtures thereof.

In certain embodiments, the source of electropositive metal in thepretreatment composition is a water soluble metal salt. In certainembodiments of the present invention, the water soluble metal salt is awater soluble copper compound. Specific examples of water soluble coppercompounds, which are suitable for use in the present invention include,but are not limited to, copper cyanide, copper potassium cyanide, coppersulfate, copper nitrate, copper pyrophosphate, copper thiocyanate,disodium copper ethylenediaminetetraacetate tetrahydrate, copperbromide, copper oxide, copper hydroxide, copper chloride, copperfluoride, copper gluconate, copper citrate, copper lauroyl sarcosinate,copper formate, copper acetate, copper propionate, copper butyrate,copper lactate, copper oxalate, copper phytate, copper tartarate, coppermalate, copper succinate, copper malonate, copper maleate, copperbenzoate, copper salicylate, copper aspartate, copper glutamate, copperfumarate, copper glycerophosphate, sodium copper chlorophyllin, copperfluorosilicate, copper fluoroborate and copper iodate, as well as coppersalts of carboxylic acids in the homologous series formic acid todecanoic acid, copper salts of polybasic acids in the series oxalic acidto suberic acid, and copper salts of hydroxycarboxylic acids, includingglycolic, lactic, tartaric, malic and citric acids.

When copper ions supplied from such a water-soluble copper compound areprecipitated as an impurity in the form of copper sulfate, copper oxide,etc., it may be preferable to add a complexing agent that suppresses theprecipitation of copper ions, thus stabilizing them as a copper complexin the solution.

In certain embodiments, the copper compound is added as a copper complexsalt such as K₃Cu(CN)₄ or Cu-EDTA, which can be present stably in thecomposition on its own, but it is also possible to form a copper complexthat can be present stably in the composition by combining a complexingagent with a compound that is difficultly soluble on its own. Examplesthereof include a copper cyanide complex formed by a combination of CuCNand KCN or a combination of CuSCN and KSCN or KCN, and a Cu-EDTA complexformed by a combination of CuSO₄ and EDTA.2Na.

With regard to the complexing agent, a compound that can form a complexwith copper ions can be used; examples thereof include inorganiccompounds, such as cyanide compounds and thiocyanate compounds, andpolycarboxylic acids, and specific examples thereof includeethylenediaminetetraacetic acid, salts of ethylenediaminetetraaceticacid, such as dihydrogen disodium ethylenediaminetetraacetate dihydrate,aminocarboxylic acids, such as nitrilotriacetic acid and iminodiaceticacid, oxycarboxylic acids, such as citric acid and tartaric acid,succinic acid, oxalic acid, ethylenediaminetetramethylenephosphonicacid, and glycine.

In certain embodiments, the electropositive metal, such as copper, isincluded in the pretreatment compositions in an amount of at least 1ppm, such as at least 5 ppm, or in some cases, at least 10 ppm of totalmetal (measured as elemental metal). In certain embodiments, theelectropositive metal is included in such pretreatment compositions inan amount of no more than 500 ppm, such as no more than 100 ppm, or insome cases, no more than 50 ppm of total metal (measured as elementalmetal). The amount of electropositive metal in the pretreatmentcomposition can range between any combination of the recited valuesinclusive of the recited values.

The pretreatment compositions of the present invention also comprisefree fluorine. As will be appreciated, the source of free fluorine inthe pretreatment compositions of the present invention can vary. Forexample, in some cases, the free fluorine may derive from the group IIIBand/or IVB metal compound used in the pretreatment composition, such asis the case, for example, with hexafluorozirconic acid. As the groupIIIB and/or IVB metal is deposited upon the metal substrate during thepretreatment process, fluorine in the hexafluorozirconic acid willbecome free fluorine and, as will be appreciated, the level of freefluorine in the pretreatment composition will, if left unchecked,increase with time as metal is pretreated with the pretreatmentcomposition of the present invention.

In addition, the source of free fluorine in the pretreatmentcompositions of the present invention may include a compound other thanthe group IIIB and/or IVB metal compound. Non-limiting examples of suchsources include HF, NH₄F, NH₄HF₂, NaF, and NaHF₂.

As used herein, the term “free fluorine” refers to isolated fluorine ionand its concentration in the pretreatment compositions of the presentinvention can be determined by measuring a pretreatment composition by ameter with a fluorine ion electrode. The Examples herein illustrate asuitable method for determining the concentration of free fluorine in acomposition for purposes of the present invention.

The pretreatment compositions of the present invention also comprise ametal fluoride salt formed from a metal which forms a fluoride salthaving a pK_(sp) of at least 11, in some cases at least 15, or, in yetother cases, at least 20. As will be appreciated, pK_(sp) refers to theinverse log of the solubility product constant for a compound. In thepresent invention, a metal containing compound is supplied wherein themetal is selected such that it forms a fluoride salt having a pK_(sp) ofat least 11. For purposes of the present invention, the pK_(sp) valuefor a metal fluoride salt refers to the pK_(sp) values reported inLange's Handbook of Chemistry, 15th Ed., McGraw-Hill, 1999, Table 8.6.In certain embodiments of the present invention, the metal which forms afluoride salt having a pK_(sp) of at least 11 is selected from cerium(pK_(sp) of CeF₃ is 15.1), lanthanum (pK_(sp) of LaF₃ is 16.2), scandium(pK_(sp) of ScF₃ is 23.24), yttrium (pK_(sp) of YF₃ is 20.06), or amixture thereof.

Moreover, in the compositions of the present invention, the amount ofthe metal containing compound that is supplied to form the fluoride salthaving a pK_(sp) of at least 11 is selected such that the level of freefluorine in the composition is no less than 0.1 ppm, in some cases noless than 20 ppm, and no more than 300 ppm, in some cases no more than100 ppm. As will be appreciated, and as was previously mentioned, thelevel of free fluorine in the pretreatment compositions of the presentinvention will increase over time as metal is pretreated therewith. Inthe present invention, a metal containing compound as described above issupplied to the pretreatment composition as needed to maintain the levelof free fluorine at no less than 0.1 ppm and no more than 300 ppm on thepretreatment composition.

In accordance with the present invention, the metal fluoride salt formedfrom the metal which forms a fluoride salt having a pK_(sp) of at least11 can be removed from the composition of the present invention eitherrelatively immediately upon formation thereof or, if chosen, thefluoride salt may be allowed to remain in the composition for a periodof time. What is important, for purposes of the present invention, isthat such a fluoride salt is formed and is present in the compositioneven if only briefly.

As a result, in certain embodiments of the present invention, a yttriumcontaining compound is supplied to the pretreatment composition. Inparticular, a source of yttrium added to the pretreatment composition ofthe present invention leads to the formation of yttrium fluoridecompounds, such as YF₃, through reaction with free fluorine in thecomposition. In certain embodiments, the source of yttrium in thepretreatment composition is a water soluble yttrium salt such as yttriumacetate, yttrium chloride, yttrium formate, yttrium carbonate, yttriumsulfamate, yttrium lactate and yttrium nitrate. When the yttrium is tobe added to the pretreatment composition as an aqueous solution, yttriumnitrate, a readily available yttrium compound, is a suitable yttriumsource. Other yttrium compounds suitable for use in the pretreatmentcompositions of the present invention are organic and inorganic yttriumcompounds such as yttrium oxide, yttrium bromide, yttrium hydroxide,yttrium molybdate, yttrium sulfate, yttrium silicate, and yttriumoxalate. Organoyttrium complexes and yttrium metal can also be used. Asuitable compound of cerium includes, but is not limited to, ceriumnitrate hexahydrate. A suitable compound of lanthanum includes, but isnot limited to, lanthanum nitrate hydrate.

It has been discovered that, by selecting a metal containing compoundthat comprises a metal which forms a metal fluoride salt having apK_(sp) of at least 11, the metal containing compound is more efficientin removing free fluorine from the composition than cases wherein ametal containing compound that comprises a metal which forms a metalfluoride salt having a pK_(sp) of less than 11 is used, thereby makingit easier to control the level of free fluorine in the composition. Inaddition, such as embodiments of the present invention wherein a yttriumcontaining compound is used, the resulting sludge containing the metalfluoride salt, YF₃, is considered environmentally benign since yttriumis not considered a heavy metal. As a result, the compositions of thepresent invention avoid environmental drawbacks present in some priorart metal pretreatment compositions.

In certain embodiments, the pH of the pretreatment composition rangesfrom 2.0 to 7.0, such as 3.5 to 5.5. The pH of the pretreatmentcomposition may be adjusted using, for example, any acid or base as isnecessary. In certain embodiments, the pH of the solution is maintainedthrough the inclusion of a basic material, including water solubleand/or water dispersible bases, such as sodium hydroxide, sodiumcarbonate, potassium hydroxide, ammonium hydroxide, ammonia, and/oramines such as triethylamine, methylethyl amine, or mixtures thereof.

In certain embodiments, the pretreatment composition comprises aresinous binder. Suitable resins include reaction products of one ormore alkanolamines and an epoxy-functional material containing at leasttwo epoxy groups, such as those disclosed in U.S. Pat. No. 5,653,823. Insome cases, such resins contain beta hydroxy ester, imide, or sulfidefunctionality, incorporated by using dimethylolpropionic acid,phthalimide, or mercaptoglycerine as an additional reactant in thepreparation of the resin. Alternatively, the reaction product is that ofthe diglycidyl ether of Bisphenol A (commercially available from ShellChemical Company as EPON 880), dimethylol propionic acid, anddiethanolamine in a 0.6 to 5.0:0.05 to 5.5:1 mole ratio. Other suitableresinous binders include water soluble and water dispersible polyacrylicacids as disclosed in U.S. Pat. Nos. 3,912,548 and 5,328,525; phenolformaldehyde resins as described in U.S. Pat. No. 5,662,746; watersoluble polyamides such as those disclosed in WO 95/33869; copolymers ofmaleic or acrylic acid with allyl ether as described in Canadian patentapplication 2,087,352; and water soluble and dispersible resinsincluding epoxy resins, aminoplasts, phenol-formaldehyde resins,tannins, and polyvinyl phenols as discussed in U.S. Pat. No. 5,449,415.

In these embodiments of the present invention, the resinous binder ispresent in the pretreatment composition in an amount of 0.005 percent to30 percent by weight, such as 0.5 to 3 percent by weight, based on thetotal weight of the ingredients in the composition.

In other embodiments, however, the pretreatment composition issubstantially free or, in some cases, completely free of any resinousbinder. As used herein, the term “substantially free”, when used withreference to the absence of resinous binder in the pretreatmentcomposition, means that any resinous binder is present in thepretreatment composition in an amount of less than 0.005 percent byweight. As used herein, the term “completely free” means that there isno resinous binder in the pretreatment composition at all.

The pretreatment composition may optionally contain other materials,such as nonionic surfactants and auxiliaries conventionally used in theart of pretreatment. In an aqueous medium, water dispersible organicsolvents, for example, alcohols with up to about 8 carbon atoms, such asmethanol, isopropanol, and the like, may be present; or glycol etherssuch as the monoalkyl ethers of ethylene glycol, diethylene glycol, orpropylene glycol, and the like. When present, water dispersible organicsolvents are typically used in amounts up to about ten percent byvolume, based on the total volume of aqueous medium.

Other optional materials include surfactants that function as defoamersor substrate wetting agents.

In certain embodiments, the pretreatment composition also comprises areaction accelerator, such as nitrite ions, nitrate ions, nitro-groupcontaining compounds, hydroxylamine sulfate, persulfate ions, sulfiteions, hyposulfite ions, peroxides, iron (III) ions, citric acid ironcompounds, bromate ions, perchlorinate ions, chlorate ions, chloriteions as well as ascorbic acid, citric acid, tartaric acid, malonic acid,succinic acid and salts thereof. Specific examples of suitable materialsand their amounts are described in United States Patent ApplicationPublication No. 2004/0163736 A1 at [0032] to [0041], the cited portionof which being incorporated herein by reference.

In certain embodiments, the pretreatment composition also comprises afiller, such as a siliceous filler. Non-limiting examples of suitablefillers include silica, mica, montmorillonite, kaolinite, asbestos,talc, diatomaceous earth, vermiculite, natural and synthetic zeolites,cement, calcium silicate, aluminum silicate, sodium aluminum silicate,aluminum polysilicate, alumina silica gels, and glass particles. Inaddition to the siliceous fillers other finely divided particulatesubstantially water-insoluble fillers may also be employed. Examples ofsuch optional fillers include carbon black, charcoal, graphite, titaniumoxide, iron oxide, copper oxide, zinc oxide, antimony oxide, zirconia,magnesia, alumina, molybdenum disulfide, zinc sulfide, barium sulfate,strontium sulfate, calcium carbonate, and magnesium carbonate.

In certain embodiments, the pretreatment composition comprises phosphateions. In certain embodiments, phosphate ions are present in an amount of10 to 500 ppm of phosphate ion, such as 25 to 200 ppm phosphate ion.Exemplary sources of phosphate ion include H₃PO₄, NaH₂PO₄, and/or(NH₄)H₂PO₄. In certain embodiments, however, the pretreatmentcomposition of the present invention is substantially or, in some cases,completely free of phosphate ion. As used herein, the term“substantially free” when used in reference to the absence of phosphateion in the pretreatment composition, means that phosphate ion is presentin the composition in an amount less than 10 ppm. As used herein, theterm “completely free”, when used with reference to the absence ofphosphate ions, means that there are no phosphate ions in thecomposition at all.

In certain embodiments, the pretreatment composition is substantiallyor, in some cases, completely free of chromate and/or heavy metalphosphate, such as zinc phosphate. As used herein, the term“substantially free” when used in reference to the absence of chromateand/or heavy metal phosphate in the pretreatment composition, means thatthese substances are not present in the composition to such an extentthat they cause a burden on the environment. That is, they are notsubstantially used and the formation of sludge, such as zinc phosphate,formed in the case of using a treating agent based on zinc phosphate, iseliminated. As used herein, the term “completely free”, when used withreference to the absence of a heavy metal phosphate and/or chromate,means that there is no heavy metal phosphate and/or chromate in thecomposition at all.

Moreover, in certain embodiments, the pretreatment composition issubstantially free, or, in some cases, completely free of any organicmaterials. As used herein, the term “substantially free”, when used withreference to the absence of organic materials in the composition, meansthat any organic materials are present in the composition, if at all, asan incidental impurity. In other words, the presence of any organicmaterial does not affect the properties of the composition. As usedherein, the term “completely free”, when used with reference to theabsence of organic material, means that there is no organic material inthe composition at all.

In certain embodiments, the film coverage of the residue of thepretreatment coating composition generally ranges from 1 to 1000milligrams per square meter (mg/m²), such as 10 to 400 mg/m². Thethickness of the pretreatment coating can vary, but it is generally verythin, often having a thickness of less than 1 micrometer, in some casesit is from 1 to 500 nanometers, and, in yet other cases, it is 10 to 300nanometers.

Following contact with the pretreatment solution, the substrate may berinsed with water and dried.

In certain embodiments of the methods of the present invention, afterthe substrate is contacted with the pretreatment composition, it is thencontacted with a coating composition comprising a film-forming resin.Any suitable technique may be used to contact the substrate with such acoating composition, including, for example, brushing, dipping, flowcoating, spraying and the like. In certain embodiments, however, asdescribed in more detail below, such contacting comprises anelectrocoating step wherein an electrodepositable composition isdeposited onto the metal substrate by electrodeposition.

As used herein, the term “film-forming resin” refers to resins that canform a self-supporting continuous film on at least a horizontal surfaceof a substrate upon removal of any diluents or carriers present in thecomposition or upon curing at ambient or elevated temperature.Conventional film-forming resins that may be used include, withoutlimitation, those typically used in automotive OEM coating compositions,automotive refinish coating compositions, industrial coatingcompositions, architectural coating compositions, coil coatingcompositions, and aerospace coating compositions, among others.

In certain embodiments, the coating composition comprises athermosetting film-forming resin. As used herein, the term“thermosetting” refers to resins that “set” irreversibly upon curing orcrosslinking, wherein the polymer chains of the polymeric components arejoined together by covalent bonds. This property is usually associatedwith a cross-linking reaction of the composition constituents ofteninduced, for example, by heat or radiation. Curing or crosslinkingreactions also may be carried out under ambient conditions. Once curedor crosslinked, a thermosetting resin will not melt upon the applicationof heat and is insoluble in solvents. In other embodiments, the coatingcomposition comprises a thermoplastic film-forming resin. As usedherein, the term “thermoplastic” refers to resins that comprisepolymeric components that are not joined by covalent bonds and therebycan undergo liquid flow upon heating and are soluble in solvents.

As previously indicated, in certain embodiments, the substrate iscontacted with a coating composition comprising a film-forming resin byan electrocoating step wherein an electrodepositable composition isdeposited onto the metal substrate by electrodeposition. In the processof electrodeposition, the metal substrate being treated, serving as anelectrode, and an electrically conductive counter electrode are placedin contact with an ionic, electrodepositable composition. Upon passageof an electric current between the electrode and counter electrode whilethey are in contact with the electrodepositable composition, an adherentfilm of the electrodepositable composition will deposit in asubstantially continuous manner on the metal substrate.

Electrodeposition is usually carried out at a constant voltage in therange of from 1 volt to several thousand volts, typically between 50 and500 volts. Current density is usually between 1.0 ampere and 15 amperesper square foot (10.8 to 161.5 amperes per square meter) and tends todecrease quickly during the electrodeposition process, indicatingformation of a continuous self-insulating film.

The electrodepositable composition utilized in certain embodiments ofthe present invention often comprises a resinous phase dispersed in anaqueous medium wherein the resinous phase comprises: (a) an activehydrogen group-containing ionic electrodepositable resin, and (b) acuring agent having functional groups reactive with the active hydrogengroups of (a).

In certain embodiments, the electrodepositable compositions utilized incertain embodiments of the present invention contain, as a mainfilm-forming polymer, an active hydrogen-containing ionic, oftencationic, electrodepositable resin. A wide variety of electrodepositablefilm-forming resins are known and can be used in the present inventionso long as the polymers are “water dispersible,” i.e., adapted to besolubilized, dispersed or emulsified in water. The water dispersiblepolymer is ionic in nature, that is, the polymer will contain anionicfunctional groups to impart a negative charge or, as is often preferred,cationic functional groups to impart a positive charge.

Examples of film-forming resins suitable for use in anionicelectrodepositable compositions are base-solubilized, carboxylic acidcontaining polymers, such as the reaction product or adduct of a dryingoil or semi-drying fatty acid ester with a dicarboxylic acid oranhydride; and the reaction product of a fatty acid ester, unsaturatedacid or anhydride and any additional unsaturated modifying materialswhich are further reacted with polyol. Also suitable are the at leastpartially neutralized interpolymers of hydroxy-alkyl esters ofunsaturated carboxylic acids, unsaturated carboxylic acid and at leastone other ethylenically unsaturated monomer. Still another suitableelectrodepositable film-forming resin comprises an alkyd-aminoplastvehicle, i.e., a vehicle containing an alkyd resin and an amine-aldehyderesin. Yet another anionic electrodepositable resin compositioncomprises mixed esters of a resinous polyol, such as is described inU.S. Pat. No. 3,749,657 at col. 9, lines 1 to 75 and col. 10, lines 1 to13, the cited portion of which being incorporated herein by reference.Other acid functional polymers can also be used, such as phosphatizedpolyepoxide or phosphatized acrylic polymers as are known to thoseskilled in the art.

As aforementioned, it is often desirable that the activehydrogen-containing ionic electrodepositable resin (a) is cationic andcapable of deposition on a cathode. Examples of such cationicfilm-forming resins include amine salt group-containing resins, such asthe acid-solubilized reaction products of polyepoxides and primary orsecondary amines, such as those described in U.S. Pat. Nos. 3,663,389;3,984,299; 3,947,338; and 3,947,339. Often, these amine saltgroup-containing resins are used in combination with a blockedisocyanate curing agent. The isocyanate can be fully blocked, asdescribed in U.S. Pat. No. 3,984,299, or the isocyanate can be partiallyblocked and reacted with the resin backbone, such as is described inU.S. Pat. No. 3,947,338. Also, one-component compositions as describedin U.S. Pat. No. 4,134,866 and DE-OS No. 2,707,405 can be used as thefilm-forming resin. Besides the epoxy-amine reaction products,film-forming resins can also be selected from cationic acrylic resins,such as those described in U.S. Pat. Nos. 3,455,806 and 3,928,157.

Besides amine salt group-containing resins, quaternary ammonium saltgroup-containing resins can also be employed, such as those formed fromreacting an organic polyepoxide with a tertiary amine salt as describedin U.S. Pat. Nos. 3,962,165; 3,975,346; and 4,001,101. Examples of othercationic resins are ternary sulfonium salt group-containing resins andquaternary phosphonium salt-group containing resins, such as thosedescribed in U.S. Pat. Nos. 3,793,278 and 3,984,922, respectively. Also,film-forming resins which cure via transesterification, such asdescribed in European Application No. 12463 can be used. Further,cationic compositions prepared from Mannich bases, such as described inU.S. Pat. No. 4,134,932, can be used.

In certain embodiments, the resins present in the electrodepositablecomposition are positively charged resins which contain primary and/orsecondary amine groups, such as described in U.S. Pat. Nos. 3,663,389;3,947,339; and 4,116,900. In U.S. Pat. No. 3,947,339, a polyketiminederivative of a polyamine, such as diethylenetriamine ortriethylenetetraamine, is reacted with a polyepoxide. When the reactionproduct is neutralized with acid and dispersed in water, free primaryamine groups are generated. Also, equivalent products are formed whenpolyepoxide is reacted with excess polyamines, such asdiethylenetriamine and triethylenetetraamine, and the excess polyaminevacuum stripped from the reaction mixture, as described in U.S. Pat.Nos. 3,663,389 and 4,116,900.

In certain embodiments, the active hydrogen-containing ionicelectrodepositable resin is present in the electrodepositablecomposition in an amount of 1 to 60 percent by weight, such as 5 to 25percent by weight, based on total weight of the electrodeposition bath.

As indicated, the resinous phase of the electrodepositable compositionoften further comprises a curing agent adapted to react with the activehydrogen groups of the ionic electrodepositable resin. For example, bothblocked organic polyisocyanate and aminoplast curing agents are suitablefor use in the present invention, although blocked isocyanates are oftenpreferred for cathodic electrodeposition.

Aminoplast resins, which are often the preferred curing agent foranionic electrodeposition, are the condensation products of amines oramides with aldehydes. Examples of suitable amine or amides aremelamine, benzoguanamine, urea and similar compounds. Generally, thealdehyde employed is formaldehyde, although products can be made fromother aldehydes, such as acetaldehyde and furfural. The condensationproducts contain methylol groups or similar alkylol groups depending onthe particular aldehyde employed. Often, these methylol groups areetherified by reaction with an alcohol, such as a monohydric alcoholcontaining from 1 to 4 carbon atoms, such as methanol, ethanol,isopropanol, and n-butanol. Aminoplast resins are commercially availablefrom American Cyanamid Co. under the trademark CYMEL and from MonsantoChemical Co. under the trademark RESIMENE.

The aminoplast curing agents are often utilized in conjunction with theactive hydrogen containing anionic electrodepositable resin in amountsranging from 5 percent to 60 percent by weight, such as from 20 percentto 40 percent by weight, the percentages based on the total weight ofthe resin solids in the electrodepositable composition.

As indicated, blocked organic polyisocyanates are often used as thecuring agent in cathodic electrodeposition compositions. Thepolyisocyanates can be fully blocked as described in U.S. Pat. No.3,984,299 at col. 1, lines 1 to 68, col. 2, and col. 3, lines 1 to 15,or partially blocked and reacted with the polymer backbone as describedin U.S. Pat. No. 3,947,338 at col. 2, lines 65 to 68, col. 3, and col. 4lines 1 to 30, the cited portions of which being incorporated herein byreference. By “blocked” is meant that the isocyanate groups have beenreacted with a compound so that the resultant blocked isocyanate groupis stable to active hydrogens at ambient temperature but reactive withactive hydrogens in the film forming polymer at elevated temperaturesusually between 90° C. and 200° C.

Suitable polyisocyanates include aromatic and aliphatic polyisocyanates,including cycloaliphatic polyisocyanates and representative examplesinclude diphenylmethane-4,4′-diisocyanate (MDI), 2,4- or 2,6-toluenediisocyanate (TDI), including mixtures thereof, p-phenylenediisocyanate, tetramethylene and hexamethylene diisocyanates,dicyclohexylmethane-4,4′-diisocyanate, isophorone diisocyanate, mixturesof phenylmethane-4,4′-diisocyanate and polymethylenepolyphenylisocyanate. Higher polyisocyanates, such as triisocyanates canbe used. An example would includetriphenylmethane-4,4′,4″-triisocyanate. Isocyanate ( )-prepolymers withpolyols such as neopentyl glycol and trimethylolpropane and withpolymeric polyols such as polycaprolactone diols and triols (NCO/OHequivalent ratio greater than 1) can also be used.

The polyisocyanate curing agents are typically utilized in conjunctionwith the active hydrogen containing cationic electrodepositable resin inamounts ranging from 5 percent to 60 percent by weight, such as from 20percent to 50 percent by weight, the percentages based on the totalweight of the resin solids of the electrodepositable composition.

In certain embodiments, the coating composition comprising afilm-forming resin also comprises yttrium. In certain embodiments,yttrium is present in such compositions in an amount from 10 to 10,000ppm, such as not more than 5,000 ppm, and, in some cases, not more than1,000 ppm, of total yttrium (measured as elemental yttrium).

Both soluble and insoluble yttrium compounds may serve as the source ofyttrium. Examples of yttrium sources suitable for use in lead-freeelectrodepositable coating compositions are soluble organic andinorganic yttrium salts such as yttrium acetate, yttrium chloride,yttrium formate, yttrium carbonate, yttrium sulfamate, yttrium lactateand yttrium nitrate. When the yttrium is to be added to an electrocoatbath as an aqueous solution, yttrium nitrate, a readily availableyttrium compound, is a preferred yttrium source. Other yttrium compoundssuitable for use in electrodepositable compositions are organic andinorganic yttrium compounds such as yttrium oxide, yttrium bromide,yttrium hydroxide, yttrium molybdate, yttrium sulfate, yttrium silicate,and yttrium oxalate. Organoyttrium complexes and yttrium metal can alsobe used. When the yttrium is to be incorporated into an electrocoat bathas a component in the pigment paste, yttrium oxide is often thepreferred source of yttrium.

The electrodepositable compositions described herein are in the form ofan aqueous dispersion. The term “dispersion” is believed to be atwo-phase transparent, translucent or opaque resinous system in whichthe resin is in the dispersed phase and the water is in the continuousphase. The average particle size of the resinous phase is generally lessthan 1.0 and usually less than 0.5 microns, often less than 0.15 micron.

The concentration of the resinous phase in the aqueous medium is oftenat least 1 percent by weight, such as from 2 to 60 percent by weight,based on total weight of the aqueous dispersion. When such compositionsare in the form of resin concentrates, they generally have a resinsolids content of 20 to 60 percent by weight based on weight of theaqueous dispersion.

The electrodepositable compositions described herein are often suppliedas two components: (1) a clear resin feed, which includes generally theactive hydrogen-containing ionic electrodepositable resin, i.e., themain film-forming polymer, the curing agent, and any additionalwater-dispersible, non-pigmented components; and (2) a pigment paste,which generally includes one or more colorants (described below), awater-dispersible grind resin which can be the same or different fromthe main-film forming polymer, and, optionally, additives such aswetting or dispersing aids. Electrodeposition bath components (1) and(2) are dispersed in an aqueous medium which comprises water and,usually, coalescing solvents.

As aforementioned, besides water, the aqueous medium may contain acoalescing solvent. Useful coalescing solvents are often hydrocarbons,alcohols, esters, ethers and ketones. The preferred coalescing solventsare often alcohols, polyols and ketones. Specific coalescing solventsinclude isopropanol, butanol, 2-ethylhexanol, isophorone,2-methoxypentanone, ethylene and propylene glycol and the monoethylmonobutyl and monohexyl ethers of ethylene glycol. The amount ofcoalescing solvent is generally between 0.01 and 25 percent, such asfrom 0.05 to 5 percent by weight based on total weight of the aqueousmedium.

In addition, a colorant and, if desired, various additives such assurfactants, wetting agents or catalyst can be included in the coatingcomposition comprising a film-forming resin. As used herein, the term“colorant” means any substance that imparts color and/or other opacityand/or other visual effect to the composition. The colorant can be addedto the composition in any suitable form, such as discrete particles,dispersions, solutions and/or flakes. A single colorant or a mixture oftwo or more colorants can be used.

Example colorants include pigments, dyes and tints, such as those usedin the paint industry and/or listed in the Dry Color ManufacturersAssociation (DCMA), as well as special effect compositions. A colorantmay include, for example, a finely divided solid powder that isinsoluble but wettable under the conditions of use. A colorant can beorganic or inorganic and can be agglomerated or non-agglomerated.Colorants can be incorporated by use of a grind vehicle, such as anacrylic grind vehicle, the use of which will be familiar to one skilledin the art.

Example pigments and/or pigment compositions include, but are notlimited to, carbazole dioxazine crude pigment, azo, monoazo, disazo,naphthol AS, salt type (lakes), benzimidazolone, condensation, metalcomplex, isoindolinone, isoindoline and polycyclic phthalocyanine,quinacridone, perylene, perinone, diketopyrrolo pyrrole, thioindigo,anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone,anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments,diketo pyrrolo pyrrole red (“DPPBO red”), titanium dioxide, carbon blackand mixtures thereof. The terms “pigment” and “colored filler” can beused interchangeably.

Example dyes include, but are not limited to, those that are solventand/or aqueous based such as phthalo green or blue, iron oxide, bismuthvanadate, anthraquinone, perylene, aluminum and quinacridone.

Example tints include, but are not limited to, pigments dispersed inwater-based or water miscible carriers such as AQUA-CHEM 896commercially available from Degussa, Inc., CHARISMA COLORANTS andMAXITONER INDUSTRIAL COLORANTS commercially available from AccurateDispersions division of Eastman Chemical, Inc.

As noted above, the colorant can be in the form of a dispersionincluding, but not limited to, a nanoparticle dispersion. Nanoparticledispersions can include one or more highly dispersed nanoparticlecolorants and/or colorant particles that produce a desired visible colorand/or opacity and/or visual effect. Nanoparticle dispersions caninclude colorants such as pigments or dyes having a particle size ofless than 150 nm, such as less than 70 nm, or less than 30 nm.Nanoparticles can be produced by milling stock organic or inorganicpigments with grinding media having a particle size of less than 0.5 mm.Example nanoparticle dispersions and methods for making them areidentified in U.S. Pat. No. 6,875,800 B2, which is incorporated hereinby reference. Nanoparticle dispersions can also be produced bycrystallization, precipitation, gas phase condensation, and chemicalattrition (i.e., partial dissolution). In order to minimizere-agglomeration of nanoparticles within the coating, a dispersion ofresin-coated nanoparticles can be used. As used herein, a “dispersion ofresin-coated nanoparticles” refers to a continuous phase in which isdispersed discreet “composite microparticles” that comprise ananoparticle and a resin coating on the nanoparticle. Exampledispersions of resin-coated nanoparticles and methods for making themare identified in United States Patent Application Publication2005-0287348 A1, filed Jun. 24, 2004, U.S. Provisional Application No.60/482,167 filed Jun. 24, 2003, and U.S. patent application Ser. No.11/337,062, filed Jan. 20, 2006, which is also incorporated herein byreference.

Example special effect compositions that may be used include pigmentsand/or compositions that produce one or more appearance effects such asreflectance, pearlescence, metallic sheen, phosphorescence,fluorescence, photochromism, photosensitivity, thermochromism,goniochromism and/or color-change. Additional special effectcompositions can provide other perceptible properties, such as opacityor texture. In certain embodiments, special effect compositions canproduce a color shift, such that the color of the coating changes whenthe coating is viewed at different angles. Example color effectcompositions are identified in U.S. Pat. No. 6,894,086, incorporatedherein by reference. Additional color effect compositions can includetransparent coated mica and/or synthetic mica, coated silica, coatedalumina, a transparent liquid crystal pigment, a liquid crystal coating,and/or any composition wherein interference results from a refractiveindex differential within the material and not because of the refractiveindex differential between the surface of the material and the air.

In certain embodiments, a photosensitive composition and/or photochromiccomposition, which reversibly alters its color when exposed to one ormore light sources, can be used. Photochromic and/or photosensitivecompositions can be activated by exposure to radiation of a specifiedwavelength. When the composition becomes excited, the molecularstructure is changed and the altered structure exhibits a new color thatis different from the original color of the composition. When theexposure to radiation is removed, the photochromic and/or photosensitivecomposition can return to a state of rest, in which the original colorof the composition returns. In certain embodiments, the photochromicand/or photosensitive composition can be colorless in a non-excitedstate and exhibit a color in an excited state. Full color-change canappear within milliseconds to several minutes, such as from 20 secondsto 60 seconds. Example photochromic and/or photosensitive compositionsinclude photochromic dyes.

In certain embodiments, the photosensitive composition and/orphotochromic composition can be associated with and/or at leastpartially bound to, such as by covalent bonding, a polymer and/orpolymeric materials of a polymerizable component. In contrast to somecoatings in which the photosensitive composition may migrate out of thecoating and crystallize into the substrate, the photosensitivecomposition and/or photochromic composition associated with and/or atleast partially bound to a polymer and/or polymerizable component inaccordance with certain embodiments of the present invention, haveminimal migration out of the coating. Example photosensitivecompositions and/or photochromic compositions and methods for makingthem are identified in U.S. application Ser. No. 10/892,919 filed Jul.16, 2004, incorporated herein by reference.

In general, the colorant can be present in the coating composition inany amount sufficient to impart the desired visual and/or color effect.The colorant may comprise from 1 to 65 weight percent, such as from 3 to40 weight percent or 5 to 35 weight percent, with weight percent basedon the total weight of the composition.

After deposition, the coating is often heated to cure the depositedcomposition. The heating or curing operation is often carried out at atemperature in the range of from 120 to 250° C., such as from 120 to190° C., for a period of time ranging from 10 to 60 minutes. In certainembodiments, the thickness of the resultant film is from 10 to 50microns.

As will be appreciated by the foregoing description, the presentinvention is directed to compositions for treating a metal substrate.These compositions comprise: (a) a group IIIB and/or IVB metal; (b) anelectropositive metal; (c) 0.1 to 300 parts per million (“ppm”) of freefluorine; (d) a metal fluoride salt formed from a metal which forms afluoride salt having a pK_(sp) of at least 11; and (e) water. Thecomposition, in certain embodiments, is substantially free of heavymetal phosphate, such as zinc phosphate, and chromate.

In yet other respects, the present invention is directed to compositionsfor treating a metal substrate that comprise: (a) a group IIIB and/orIVB metal; (b) 0.1 to 300 ppm of free fluorine; (c) a metal fluoridesalt formed from a metal which forms a fluoride salt having a pK_(sp) ofat least 11; and (d) water. These compositions of the present inventionare substantially free of phosphate ions and chromate.

As has been indicated throughout the foregoing description, the methodsand coated substrates of the present invention do not, in certainembodiments, include the deposition of a crystalline phosphate, such aszinc phosphate, or a chromate. As a result, the environmental drawbacksassociated with such materials can be avoided. Nevertheless, the methodsof the present invention have been shown to provide coated substratesthat are, in at least some cases, resistant to corrosion at a levelcomparable to, in some cases even superior to, methods wherein suchmaterials are used. This is a surprising and unexpected discovery of thepresent invention and satisfies a long felt need in the art.

Illustrating the invention are the following examples that are not to beconsidered as limiting the invention to their details. All parts andpercentages in the examples, as well as throughout the specification,are by weight unless otherwise indicated.

EXAMPLES

Fluoride ion concentration, including both free and total fluoride, canbe measured using a variety of methods familiar to those skilled in theart. Frequently, fluoride ion concentration is measured using anion-selective electrode (“ISE”), such as the sympHony® Fluoride IonSelective Combination Electrode supplied by VWR International, orsimilar electrodes. The fluoride ISE is standardized by immersing theelectrode into solutions of known fluoride concentration and recordingthe reading in millivolts; then, plotting these millivolt readings in alogarithmic graph. The millivolt reading of an unknown sample can thenbe compared to this calibration graph and the concentration of fluoridedetermined. Alternatively, the fluoride ISE can be used with a meterthat will perform the calibration calculations internally and thus,after calibration, the concentration of the unknown sample can be readdirectly.

Fluoride ion is a small negative ion with a high charge density, so inaqueous solution it is frequently complexed with metal ions having ahigh positive charge density, such as zirconium or titanium, or withhydrogen ion. The fluoride ions thus complexed are not measurable withthe fluoride ISE unless the solution they are present in is mixed withan ionic strength adjustment buffer that releases the fluoride ions fromsuch complexes. At that point the fluoride ions are measurable by thefluoride ISE, and the measurement is known as “total fluoride”. Afluoride measurement taken without using such a reagent is known as“free fluoride”, since it is only the fluoride ion not bound withhydrogen ion or in metal complexes.

For purposes of the Examples that follow, the fluoride was measured asfollows: The calibration standards were prepared by adding 2 mL each ofstandard solutions containing, respectively, 100 ppm, 300 ppm and 1000ppm of fluoride ion, to 50 mL of an ionic strength adjustment buffercomprised of 10% by weight sodium citrate dihydrate (available fromAldrich Chemical, Milwaukee, Wis.) in deionized water. The millivoltreading of each of these standards were then measured with a fluorideISE and used to construct a calibration curve as described above. Fortotal fluoride values, 2 mL of the unknown solution was mixed with 50 mLof the sodium citrate buffer and the millivolt reading of the fluorideISE of this solution was compared with the calibration curve generatedto determine the total fluoride. Free fluoride was determined bydirectly reading the millivolts of the sample solution and comparingwith the calibration curve, and then dividing this number by 26 (thedivision was necessary since the standards were diluted by a factor of26 due to the ionic strength adjustment buffer, and the free fluoridesample was not).

Example 1

A 12 L zirconium pretreatment bath was prepared as follows: 10.5 g of45% hexafluorozirconic acid (available commercially from HoneywellSpecialty Chemicals, Morristown, N.J.) and 17.57 g of a 5% w/w solutionof copper nitrate hemipentahydrate (available commercially from FisherScientific, Fair Lawn, N.J.) were added to approximately 12 liters oftap water. The solution was neutralized to pH 4.5 with Chemfil Buffer (amild alkaline buffering agent available commercially from PPGIndustries, Euclid, Ohio). The free fluoride was measured with an ISE asdescribed above and a value of 22 ppm free fluoride was obtained.

A cleaned cold rolled steel (CRS) panel was processed in this solutionat 80° F. for two minutes with moderate mixing. The panel had a bronzeappearance with some blue iridescence and the coating thickness wasmeasured using a portable X-ray fluorescence instrument (XRF) atapproximately 43 nm.

To the zirconium pretreatment solution, 16.8 g of Chemfos AFL (a liquidfree fluoride additive available from PPG Industries, Euclid, Ohio) wasthen added. This addition caused the pH to drop slightly to 3.8. The pHof the solution was adjusted back to 4.5 with Chemfil Buffer. The freefluoride was measured as previously and found to be 170 ppm. A cleanedCRS panel was then processed through this bath identically to theprevious panel. This panel had a light bronze appearance, and estimatedcoating thickness as measured by XRF was 20 nm. The presence of thehigher level of free fluoride therefore diminished the coating thicknessby greater than 50%.

At this point, 3.02 g of yttrium nitrate hexahydrate (available fromAcros Organics, a subsidiary of Fisher Scientific) was added to thezirconium pretreatment solution. This caused a slight pH drop to pH 4.3.This was adjusted back to 4.5 with Chemfil Buffer. The free fluoride wasmeasured as above and determined to be 115 ppm. A cleaned CRS panelprocessed as above had a medium bronze color with some blue iridescence,and the coating thickness as determined by XRF was approximately 31 nm.The pretreatment bath was somewhat hazy, presumably indicating theprecipitation of yttrium fluoride compounds.

Another 3.06 g of yttrium nitrate hexahydrate was added to the zirconiumpretreatment bath, which caused the pH to drop slightly to 4.2. The pHwas returned to 4.5 with the addition of Chemfil Buffer. The freefluoride, measured as above, was 61 ppm, and the pretreatment bath hadadditional precipitate. A cleaned CRS panel processed through thepretreatment bath as above had a similar appearance to the previouspanel. The coating thickness was determined via XRF to be approximately45 nm.

A further 2.98 g of yttrium nitrate hexahydrate was added to thezirconium pretreatment bath. The pH of the bath dropped slightly to 4.2;sufficient Chemfil Buffer was added to return the pH to 4.5. The freefluoride was measured as above and found to be 24 ppm, which was closeto the starting value. A cleaned CRS panel was processed as above. Thepanel was blue in appearance with some iridescence. The coatingthickness as measured with XRF was approximately 61 nm.

Example 2

A 4 liter zirconium pretreatment bath was prepared as follows: 3.5 g of45% hexafluorozirconic acid and 5.84 g of a 5% w/w solution of coppernitrate hemipentahydrate were added to approximately 4 liters of tapwater, to give a solution with 175 ppm Zr and 20 ppm Cu. The solutionwas neutralized to pH 4.5 with Chemfil Buffer. The free fluoride of thissolution was measured at 22 ppm. The solution temperature was 82° F. Twoliters of this solution was drawn off and used to pretreat a cleaned CRSpanel for two minutes. The panel was a medium bronze color inappearance, and the coating thickness was found to be approximately 28nm using the portable XRF instrument.

To this 2 liter bath was added 6 g of Chemfos AFL. The pH droppedslightly, to 3.8. Chemfil Buffer was added dropwise to return thesolution to pH 4.5. The free fluoride was now measured to be 320 ppm. Acleaned CRS panel processed through this bath for 2 minutes hadvirtually no visible pretreatment; using XRF, the thickness was measuredat 4 nm.

To this solution was added lanthanum nitrate hydrate (availablecommercially from Aldrich Chemical, Milwaukee, Wis.; 32% La). Thesolution, which had been slightly hazy to this point, clouded upinstantly. The pH, which dropped to 3.3 upon addition of the lanthanumnitrate, was adjusted back to 4.5 with Chemfil Buffer. Free fluoride wasmeasured at 31 ppm. A cleaned CRS panel processed through this bath fortwo minutes was bronze-colored with blue iridescence, and had a coatingthickness of 25 nm as measured by XRF.

Example 3

The remaining two-liter portion of the original 4 L bath was used toprocess a cleaned CRS panel for two minutes. This panel had a mediumbronze color and the zirconium pretreatment coating was measured to beapproximately 27 nm thick. To this bath was added 6 g of Chemfos AFL.The pH dropped slightly to 3.7, and was adjusted back to 4.5 withdropwise addition of Chemfil Buffer. The free fluoride of this bath wasnow measured at 316 ppm. A cleaned CRS panel processed through this bathfor 2 minutes had little visible pretreatment; using XRF, the thicknesswas measured at 5 nm.

To this solution was added cerium nitrate hexahydrate (availablecommercially from Alfa Aesar, Ward Hill, Mass.). The solution, which hadbeen slightly hazy to this point, clouded up instantly. The pH, whichdropped to 3.3 upon addition of the cerium nitrate, was adjusted back to4.5 with Chemfil Buffer. Free fluoride was measured at 28 ppm. A cleanedCRS panel processed through this bath for two minutes was bronze-coloredwith blue iridescence, and had a coating thickness of 29 nm as measuredby XRF.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications which are within the spirit and scopeof the invention, as defined by the appended claims.

1. A method for treating a metal substrate comprising contacting thesubstrate with a pretreatment composition comprising: (a) a group IIIBand/or IVB metal; (b) an electropositive metal; (c) free fluorine; (d) ametal fluoride salt formed from a metal which forms a fluoride salthaving a pK_(sp) of at least 11; and (e) water, wherein the metal thatforms the metal fluoride salt having a pK_(sp) of at least 11 issupplied in an amount sufficient to maintain the level of free fluorinein the composition to no less than 0.1 ppm and no more than 300 ppm. 2.The method of claim 1, wherein the metal substrate comprises cold rolledsteel, hot rolled steel, hot-dipped galvanized steel, galvanealed steel,and/or steel plated with zinc alloy.
 3. The method of claim 1, whereinthe group IIIB and/or IVB metal comprises zirconium.
 4. The method ofclaim 1, wherein the group IIIB and/or IVB metal is present in thepretreatment composition in an amount of at least 100 ppm metal.
 5. Themethod of claim 1, wherein the electropositive metal comprises nickel,copper, silver, and/or gold.
 6. The method of claim 1, wherein theelectropositive metal is included in the pretreatment composition in anamount of at least 10 ppm of total metal measured as elemental metal. 7.The method of claim 1, wherein the free fluorine is derived fromhexafluorozirconic acid.
 8. The method of claim 1, wherein the metalfluoride salt formed from a metal which forms a fluoride salt having apK_(sp) of at least 11 comprises yttrium.
 9. The method of claim 1,wherein the metal that forms the metal fluoride salt having a pK_(sp) ofat least 11 is supplied in an amount sufficient to maintain the level offree fluorine in the composition to no less than 0.1 ppm and no morethan 100 ppm.
 10. The method of claim 1, wherein the pretreatmentcomposition is substantially free of phosphate ions.
 11. The method ofclaim 1, wherein the pretreatment composition is substantially free ofchromate and/or zinc phosphate.
 12. The method of claim 1, furthercomprising contacting the substrate with a coating compositioncomprising a film-forming resin, wherein the contacting comprises anelectrocoating step wherein an electrodepositable composition isdeposited onto the metal substrate by electrodeposition.
 13. Acomposition for treating a metal substrate comprising: (a) a group IIIBand/or IVB metal; (b) an electropositive metal; (c) 0.1 to 300 ppm offree fluorine; (d) a metal fluoride salt formed from a metal which formsa fluoride salt having a pK_(sp) of at least 11; and (e) water.
 14. Thecomposition of claim 13, wherein the free fluorine is present in thecomposition in an amount of no less than 0.1 ppm and no more than 100ppm.
 15. The composition of claim 13, wherein the group IIIB and/or IVBmetal comprises zirconium.
 16. The composition of claim 13, wherein thegroup IIIB and/or IVB metal is present in the pretreatment compositionin an amount of at least 100 ppm metal.
 17. The composition of claim 13,wherein the electropositive metal comprises nickel, copper, silver,and/or gold.
 18. The composition of claim 13, wherein theelectropositive metal is included in the pretreatment compositions in anamount of at least 10 ppm of total metal measured as elemental metal.19. The composition of claim 13, wherein the pretreatment composition issubstantially free of phosphate ions.
 20. A composition for treating ametal substrate comprising: (a) a group IIIB and/or IVB metal; (b) 0.1to 300 ppm of free fluorine; (c) a metal fluoride salt formed from ametal which forms a fluoride salt having a pK_(sp) of at least 11; and(d) water, wherein the composition is substantially free of phosphateions and chromate.